Zhang disappeared on June 9, and was last seen on surveillance camera getting into a car now believed to be Christensen’s. Police found the car last week, but still have not located Christensen.

The suspect was reportedly under surveillance when the FBI overheard him speaking about kidnapping the Zhang. According to an Associated Press report, investigators believe that Zhang did not survive based on what they heard Christensen say, along with additional, unspecified details of the investigation.

The Daily Mail reports that investigators found on the suspect’s cell phone that he had spent time on the website FetLife, a ‘social network for the BDSM, fetish and kinky community,” and participated in threads connected to phrases like ‘Abduction 101’, ‘perfect abduction fantasy’ and ‘planning a kidnapping.’

The News-Gazette reports that Christensen said he was married and in an open relationship on a dating profile, and that he regularly worked out with an unknown woman at a gym in Champaign, Illinois.

“Most of us who were working out were usually talkative and in a good mood, but Christensen was different,” said a man who worked out at the same time. “He and the woman always wore black, and they kept to themselves. They never said anything to the rest of us.”